The present invention relates to a heat treatment apparatus and a heat treatment method for carrying out a heat treatment in a magnetic field. More specifically, the invention relates to a heat treatment apparatus for applying a heat treatment in a high magnetic field to a finely patterned material or magnetic material, particularly a magnetic material such as an MR film, a GMR film or a TMR film.
A magnetic film, such as a thin film of an Fe—Ni, Pt—Mn or Co—Fe alloy or the like, formed on a substrate by sputtering or the like, which is a magnetic material used for a magnetic head, an MRAM (Magnetic Random Access Memory) which is one of non-volatile memories or the like, can exhibit its magnetic properties by subjecting it to a heat treatment in a high magnetic field.
For this purpose, there is conventionally proposed a heat treatment apparatus in which an electric furnace, an induction heating furnace or the like is disposed to apply a heat treatment in a magnetic field formed with electromagnets or permanent magnets. A schematic configuration of a typical conventional heat treatment apparatus is illustrated in FIG. 10.
As shown in FIG. 10, a heat treatment apparatus 1A has a cylindrical vacuum vessel 2 serving as a heat treatment vessel, a holding device 3 which holds an object to be heat-treated such as a magnetic material (hereinafter referred to as the “object of treatment”) in the vacuum vessel 2, and a magnetic field generating device 20 arranged outside the vacuum vessel 2. The holding device 3 has a holder 3A which holds the object of treatment and a holder supporting unit 3B which supports the holder 3A and has a lid member 4 for opening/closing an upper opening of the vacuum vessel 2. Namely, the holder supporting unit 3B is arranged above the vacuum vessel 2, and the holder 3A holding the object of treatment is charged into the vessel by this supporting unit 3B.
The magnetic field generating device 20 is provided with a pair of electromagnets 21 arranged oppositely outside the vacuum vessel 2, and the electromagnet 21 has a magnetic core 22 and a coil 23.
A heating device 100 is provided between the outer surface of the vacuum vessel 2 and the end face of the magnetic core 22 of the electromagnet 21. Usually, the heating device 100 is spaced apart from the outer surface of the vacuum vessel 2 by a prescribed distance, and comprises an electric heater 101 arranged so as to surround the outer peripheral surface of the vacuum vessel 2. The electric heater 101 is configured as shown in the drawing, for example. That is, a spiral groove 103, for example, is provided on the inner peripheral surface of a heater support 102 facing the outer peripheral surface of the vacuum vessel. The heater support 102 is made of bricks or ceramics, and arranged so as to surround the vacuum vessel 2. And, a heating wire such as a nichrome wire 104 is positioned in the groove 103. A heat insulator 105 such as alumina felt or bricks is arranged on the outer peripheral surface of the heater support 102, so that the heat of the heating device 100 is not transferred to the electromagnets 21.
The heat-treated object is taken up from the vacuum vessel 2. Then, a new object of treatment is held by the holder 3A, charged by the supporting unit 3B into the vacuum vessel 2 from above, and subjected to the above-mentioned heat treatment. Subsequently, the heat treatment of the object of treatment is continued by batch treatment with the same procedure.
In the conventional heat treatment apparatus 1A, since a magnetic material or the like as the object of treatment has a large weight, the upper end of the vacuum vessel 2 has an opening, and the object of treatment is charged into, and discharged from, the vacuum vessel 2 through this opening.
According to the results of studies and experiments carried out by the present inventor, although the heat treatment apparatus 1A having the above-mentioned configuration is configured so as to carry out a heat treatment in a dust-free environment, deposition of dust onto the object of treatment was observed.
Further studies were carried out to solve this problem, and the results revealed the following. The conventional heat treatment apparatus 1A has the supporting unit 3B, and in addition, although not shown in FIG. 10, a moving device, such as a lift mechanism having a driving motor for vertically moving the supporting unit 3B, arranged above the object of treatment held by the holder 3A and the vacuum vessel 2. Upon operation, therefore, dust produced from the supporting unit 3B and the moving device adheres directly to the object of treatment or further intrudes into the vacuum vessel 2 to deposit onto the object of treatment during the heat treatment.
In order to prevent generation of dust from the holder supporting unit 3B and the moving device, therefore, it is necessary to extensively make efforts to eliminate dust from the entire apparatus, and this requires a more complicated and larger-scaled apparatus structure. This results in a larger space for installation of the apparatus and in a lower degree of freedom in the apparatus arrangement.
The present inventor therefore proposed, in Japanese Patent Application No. 2002-48634, a heat treatment apparatus in which it is hard for dust to adhere to the object of treatment, and a heat treatment method therefor.
More specifically, as shown in FIG. 11, a treatment chamber 50 for charging and discharging the object of treatment into and from the vacuum vessel 2 is arranged under the vacuum vessel 2. The object of treatment is moved up and down by the moving device 10 via the holder supporting unit 3B and the holder 3A, thereby the object of treatment displaces between the heat treatment vessel 2 and the treatment chamber 50.
The above-mentioned configuration in which the moving device 10 for moving the object of treatment and the like are arranged below the vacuum vessel 2, provides advantages in making it difficult for dust to adhere to the object of treatment.
On the other hand, with respect to objects of treatment, magnetic material wafers, for example, 8-inch-sized (having a diameter of about 200 mm) wafers are commonly used at present, as the wafers to be charged into the heat treatment apparatuses. Recently, however, in terms of the operating efficiency, there is an increasing demand for larger wafers, that is, 12-inch-sized (diameter of about 300 mm) wafers.
When using the heat treatment apparatus having a so-called vertical tubular furnace as shown in FIG. 11, it is of course necessary to increase the diameter of the heat treatment vessel 2 sufficiently to house 12-inch-sized wafers. However, in this case, the magnetic field generating device 20 for generating the magnetic field having the field direction perpendicular to the longitudinal direction of the furnace core tube, i.e., a pair of electromagnets becomes larger in size. Also, when maintaining treatment number of wafers as in the conventional art, the magnet should further be increased in size.
This inevitably leads to a largely increased total height of the heat treatment apparatus and an increased weight of the electromagnet, along with the increase in size of the magnet. The base supporting the magnet must also necessarily have a larger and stronger structure.
The installation area and the volume of the heat treatment apparatus are therefore increased. As a result, it is very difficult or even impossible to install and use the apparatus in a conventional clean room, thus requiring construction of a new clean room of special specifications.